Review of U.S. Department of Transportation Truck Size and Weight Study - Second Report: Review of USDOT Technical Reports (2015) / Chapter Skim
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Pages 25-34
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From page 25... ...
23 3. BRIDGES The MAP-21 Section 32801 study charge requires the USDOT study to evaluate the impacts on the infrastructure (including bridges)
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From page 26... ...
24 Responsiveness to the Questions Identified by Congress The response of the bridge analysis to the legislative charge is incomplete on account of the following omissions: Missing costs (as identified in the following section) ; Lack of a comprehensive framework that would allow the reader to put the USDOT study's impact estimates in perspective with respect to total bridge-related costs and the factors that determine costs; and Lack of estimates of bridge impacts of grandfather and other exemptions from federal limits in the states where the exemptions apply, and lack of evaluation of the ability of each state in which exempt trucks operate to recover the costs of the trucks' bridge impacts.
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From page 27... ...
25 Bridge deck costs: The USDOT report states: "It was not possible to draw national conclusions or present findings concerning the effect on overall bridge service life. While it is highly likely that bridge deck deterioration will accelerate with additional or heavier axle loads, the complex relationship of parameters that determine that performance is not well-defined."5 User costs of delay at bridge construction projects or for detours around posted bridges: Even bridges that states selected for eventual strengthening or replacement would be posted for some time, until funds became available for construction.
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From page 28... ...
26 Because of these omissions, the USDOT study provides little information to policy makers about bridge costs, which the past USDOT and TRB truck size and weight studies have concluded would be the major infrastructure impact of changes in truck size and weight limits. Credible estimates of the order of magnitude of the missing costs would have been possible, based on methods used in past studies and reasonable assumptions, and sensitivity analyses could have been used to illustrate the degree of uncertainty in the costs.
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From page 29... ...
27 The TRB Truck Weight Limits (TRB 1990a, 102–104) and Turner proposal (TRB 1990b, 152)
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28 Bridge Sample The report contains only a general description of how the sample of 490 bridges was selected. USDOT explained to the committee that the bridges were sought and selected to make the sample appear representative with respect to age, span length, and other features.
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From page 31... ...
29 Unit Costs The bridge replacement and strengthening cost estimates in the USDOT study assume an average cost of $235 per square foot, derived from records of federal-aid project costs. The report does not describe the derivation of this cost, the variability in costs from project to project, or the mix of strengthening projects and replacement projects in the data from which it was derived.
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From page 32... ...
30 appropriate for the purpose of the study. However, the report does not adequately explain the inconsistency in the weight assumptions.
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From page 33... ...
31 Addendum to Chapter 3 Ideas are offered below on an approach for a practical but comprehensive study of bridge costs of changes in size and weight limits. The largest costs will arise from three impacts: Deck degradation leading to deck repair or replacement, Loads exceeding the strength of main load-carrying members, and Increased cost of future bridges.
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From page 34... ...
32 Future bridges may need deeper cross sections to carry an alternative configuration. A modified table of depth-to-span ratios for each structure type would need to be developed for each of the scenario vehicles.
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